Recently a great deal of attention has been given to the level of emissions generated by internal combustion engines, as well as their efficiency. In order to increase the efficiency of these engines and reduce their harmful emissions, fuel injectors have been developed for metering the fuel supplied to the engine.
In general, these fuel injectors include a body having a solenoid operated flow valve. Biasing means such as a spring apply a force to a body of the valve for closing the valve, while when activated the solenoid overcomes the spring force to open the valve.
Fuel is supplied under high pressure to the fuel injector, such as with a high pressure pump. When the valve of the injector is opened, the fuel flows therethrough to the engine.
A problem associated with this valve is that the range of opening time of the valve of the injector can not be controlled with infinite precision. In particular, the momentum of the mass of the valve body, spring and the like serve to limit the rate of speed with which the valve may be opened and reclose. A typical minimum working, duration may be about 1 ms.
At this long minimum working duration, maximum fuel delivery benefits are generally only achieved when the engine speed is less than about 1000 rpm. When the engine speed is above this speed, as is very common with today's engines, the duration during which fuel is delivered to the engine during a given cycle is longer than the desired fuel injection duration.
One manner to decrease the working duration in this type of valve is to decrease the pressure at which the fuel is delivered. This permits the valve to close somewhat faster. On the other hand, this solution has the attenuated problem that the low fuel pressure may not permit atomization of the fuel which is injected, reducing the burn efficiency and thus overall engine efficiency and emissions benefits.
It is an object of the present invention to provide a fuel injection system which provides for a large dynamic range of injection time, permitting the fuel injection time to be varied over a wide time duration. It is a further object of the present invention to provide a fuel injection system which permits accurate control of the volume of fuel delivered and the time of delivery thereof.